Peter V. Nielsen, Li Rong and Inés Olmedo The IEA Annex 20 Two ...

Figure 7. Probability density function of ufloor at x/H = 1.0. See [8].The probability density function of uuouoclose to the ceiling at x/H = 2.0, and close to theclose to the ceiling at x/H = 2.0 has a well-definedmean velocity, and the velocity fluctuates around the mean velocity in a symmetricaldistribution, figure 7A, while the flow close to the floor at x/H = 1.0 is asymmetric (has askewness) with a probability of both a negative and a positive velocity, figure 7B.Different turbulence modelsTwo-dimensional steady state predictions with different turbulence models indicate somedifferences, especially in two of the corners as shown in figure 8, [9]. The grid is identical inall four cases, which means that the difference in the flow can be ascribed to the turbulencemodels used to predict the two-dimensional flow. The predictions with the SST model showespecially a large recirculating flow in the occupied zone below the supply slot 0 < x/H < 1.5.Similar results have been obtained by Voigt [10]. It is not possible to fully exclude this flowpattern from the observation of the streaklines shown by photos as in figure 2, but it does notcorresponds to the Laser-Doppler measurements in the benchmark.Figure 8. Two-dimensional isothermal and steady state simulations of the Annex 20 2Dbenchmark test. Four different turbulence models are used together with the RANS equations.THREE-DIMENSIONAL STEADY STATE PREDICTIONSThe benchmark was originally selected for the simulation of steady two-dimensional flows forthe IEA Annex 20 work back in 1990. The flow in the benchmark was considered to be twodimensionaland steady, but three-dimensional unsteady flows could, at least in principle,occur. LES predictions indicate an asymmetric probability density function at the floor at x/H= 1.0 with a probability of both negative and positive velocities, figure 7B, and measurementsin rooms with L/H ≥ 4.0 and W/H = 4.7 do also show unsteady flow at the floor for 0 < x/H